The present invention relates to a reception field detection apparatus for detecting the signal intensity of a reception signal in a radio frequency band and, more particularly, to a reception field detection apparatus suitably used in a mobile communication base station of a mobile telephone system or the like which receives radio signals of a plurality of channels.
In a mobile communication base station of a conventional mobile telephone system or the like, in general, radio signals transmitted from a plurality of mobile units for the respective channels are received by corresponding receivers, the signal intensity of the received radio signals are measured by reception field detection apparatuses respectively incorporated in the receivers, and the channel connection control or the like of the system is performed in accordance with the signal intensity of the received radio signal. In the base station, the radio signals of all the channels received by an antenna are supplied to a signal distributer arranged in the station, and the received radio signals are distributed to the receivers, respectively. In the base station, the radio signal intensity received by each receivers must be accurately compared with each other for the channel connection control. An appropriate point such as the input terminal of the distributer or the output terminal of the antenna is set as a reception input definition point, and a received radio signal intensity at the reception input definition point is set as the standard of the received radio signal intensity (or reception field intensity) of the receivers.
In this case, the signal distributer and the receivers are connected to each other through a signal transmission line of each channel. The losses of the signal transmission lines change depending on the lengths and channels (frequencies) of the signal transmission lines. In addition, the distribution losses at the output terminals of the signal distributer are often different from each other. Therefore, when the input terminal of the signal distributer is set as the reception input definition point, and radio signal intensity of all the channels are equal to each other at this input terminal, radio signal intensity measured at the input terminals of the receivers are often different from each other. For this reason, in the reception field detection apparatus of each receiver, a measured signal intensity must be corrected for each receiver, and the conditions of objects to be compared must coincide with each other.
In such a conventional reception field detection apparatus, differences in measured signal intensity detected at the input terminals of the receivers are corrected by a fixed value (for example, Japanese Patent Laid-Open No. 4-342321: Reception Field Detection Apparatus for Radio Transceiver, and Japanese Patent Laid-Open No. 4-266223: Radio Receiver).
In the conventional reception field detection apparatus described above, a correction value of the signal intensity for each receiver is fixed to a value adjusted at an initial state. For this reason, even when a value to be corrected being changed due to a change in mounting position of each receiver on the rack installed in the station in an operation state, deterioration of each field intensity detection circuit over time, or the like, the correction value for an accurate measurement of the signal intensity cannot be easily changed.